In the preferred applications the final control of the gas flow to an engine is typically by a venturi (carburation system) or a solenoid valve (fuel injection system). Both of these require precise and accurate control of the input pressure to the device. In automotive use the pressure in the fuel storage container may range from 0.6 MPa to over 30 MPa (90 to 4500 psig) necessitating the use of sophisticated regulation systems to achieve a constant output pressure with the requisite variable mass flow rate.
The known regulators are mechanical. These regulators are preset by the manufacturer and may be difficult to adjust correctly after installation. Recent automotive regulations in many countries prohibit adjustment to a regulator after installation as tampering with the emission system. This requires that the regulator remains in tolerance for long periods, normally amounting to a number of years or a representative cumulative distance.
Existing natural gas vehicle (NGV) regulators for fuel injection applications are mechanical systems with either one or two stages of pressure regulation. Three or four stages of pressure regulation are used in conventional carburetor-mixer NGV fuel systems. Mechanical regulators can be designed to address many of the problems, but this may increase the number of moving parts, which in turn may affect reliability and cost. Although these systems have demonstrated good performance in many applications, there are problems associated with their use.
Droop: One difficulty with mechanical regulators is that the output pressure decreases or droops, when the fuel flow rate is increased significantly, which frequently happens in automotive applications. Typically, the fuel flow rate increases by a factor of 30 on acceleration from idle to maximum engine speed at wide open throttle. This can cause pressure droop between 70 and 140 kPa (10 to 20 psig) for mechanical regulators. Pressure droop complicates the calibration of fuel injected engines because there must be compensation for the pressure reduction in the calibration tables to maintain a proper air fuel ratio. Systems with droop require sophisticated and expensive compensation systems.
Resonance: The spring and diaphragm arrangement in a mechanical regulator may be sensitive to resonance. The flow dynamics of the manifold that connects the fuel injectors to the regulator can be prone to pressure resonances of 70 to 210 kPa (10 to 30 psig).
Hysteresis: The spring and diaphragm arrangement in a mechanical regulator may be sensitive to hysteresis which can result in a pressure reduction of 70 kPa (10 psig).
Temperature: The spring and diaphragm arrangement in a mechanical regulator may be sensitive to temperature effects. Elastomeric diaphragms are less flexible in cold weather, which decreases the ability of the fueling system to respond to changes in vehicle operation.
Transient response:
Mechanically regulated systems cannot compensate for the inertial lag from injectors on fuel injected natural gas vehicles. Current injectors have an opening time of up to 4 milliseconds, which is a significant portion of their pulse width operation.
The present invention aims at a system that ameliorates the problems with the mechanical regulators of the prior art.